1. Field of the Invention
This invention relates to fluid torque transmission devices. More specifically, the present invention relates to fluid torque transmission devices equipped with lockup devices such as torque converters and fluid couplings.
2. Background Information
A torque converter has three types of vane discs (impeller, turbine, and stator) therein to transmit torque via hydraulic oil. The impeller is affixed to a front cover as an input side rotating member. The turbine is placed in the fluid chamber facing the impeller. As the impeller rotates, the hydraulic oil flows to the turbine from the impeller and outputs the torque by means of rotating the turbine.
The lockup device is placed in a space between the turbine and the front cover. The lockup device is a mechanism for directly transmitting the torque from the front cover to the turbine by means of mechanically connecting the front cover with the turbine.
A conventional lockup device normally includes a disk-like piston, a retaining plate, a torsion spring, and a driven plate. The disk-like piston can be pressed against the front cover. The retaining plate is affixed to the outer periphery of the piston. The torsion spring is supported in a rotational direction on the outer periphery by the retaining plate. The driven plate supports both ends of the torsion spring in the rotational direction. The driven plate is affixed to a turbine shell.
When the lockup device engages with the front cover, torque is transmitted from the front cover to the piston, and then to the turbine via the torsion spring. Further, in the elastic connection mechanism of the lockup device, the torsion spring is compressed in the rotational direction between the retaining plate and the driven plate to absorb and dampen twisting vibrations.
There are two kinds of torsion vibration noises, primarily, i.e., running noises (booming noise, etc.) and shock or jerking noises (low frequency vibrations).
The former kind of noises is generated when the rotational variations of the engine are transmitted to the drive train and develop booming sounds in the cabin through the suspension and the mounts. The damper for those noises has to be able to reduce the torsional rigidity to lower the resonance point as much as possible from the lockup region, and to achieve a high damping performance with a low hysteresis torque.
The latter kind of noises, the shock or jerking noises, is generated when the torque is inputted in a step-like manner as a result of stepping on the accelerator pedal abruptly or releasing it abruptly. As a consequence, the car body is shaken back and forth violently in a transient mode. The damper for such a phenomenon is required to have a torsional characteristic of a high hysteresis torque.
Trying to use a low hysteresis torque in order to dampen the booming sound caused by the rotational variations of the engine introduces in turn another problem, i.e., intensification of low frequency vibrations. Moreover, if a friction damping mechanism having multiple plates between the piston and the turbine is installed in the lockup device, it creates the problem of using needed springs in addition to the friction members, thus increasing the number of parts. Additionally, if a damper mechanism similar to a clutch disk assembly used in a clutch device is used, a complex friction damping mechanism is needed. The complex friction damping mechanism has friction members provided between the driven plate and the drive plates on both sides of the mechanism in the axial direction. Furthermore, the complex friction damping mechanism has springs for generating an axially energizing force. The problem here is that springs are needed in addition to the friction members, thus increasing the number of parts. In view of the above, there exists a need for a fluid torque transmission device equipped with lockup device that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the present invention is to improve the noise damping characteristics of the fluid type torque transmission device equipped with a lockup device by simultaneously damping both the running noises and the shock and/or jerking noises.
Another object of the present invention is to provide a more compact friction damping mechanism in a fluid torque converter equipped with a lockup device.
A fluid torque transmission device equipped with a lockup device in accordance with a first aspect of the present invention has a front cover, an impeller, a turbine, a lockup device, and a friction generating mechanism. The impeller constitutes a fluid chamber together with the front cover. The turbine is arranged to face axially the impeller in the fluid chamber. The lockup device is a mechanism configured for mechanically connecting and disconnecting the front cover from the turbine. The lockup device includes a clutch mechanism and an elastic connection mechanism. The friction generating mechanism is a mechanism for generating friction resistance when the lockup device is in operation. The friction generating mechanism includes a friction surface and a micro gap that prevents the friction surface from operating within a range of small twisting angles.
According to this fluid torque transmission device, the torque of the front cover is mechanically transmitted to the turbine via the lockup device of the front cover when the clutch mechanism of the lockup device is engaged. When twisting vibrations from the front cover are transmitted to the lockup device, the elastic connection mechanism of the lockup device operates to absorb and dampen the twisting vibrations. The friction surface of the friction generating mechanism engages in a rubbing action at this time and generates a specified hysteresis torque.
If the type of the twisting vibration is such that the twisting angle is quite large as in the case of a low frequency vibration, the friction surface engages in a rubbing action and causes a high hysteresis torque. Therefore, the low frequency vibration is quickly attenuated. If the type of the twisting vibration is such that the twisting angle is small as in the case of the engine speed fluctuation, which often causes abnormal sounds during driving, the friction surface does not engage in a rubbing action because of the existence of the micro twisting angle gap. Thus the friction surface does not produce a high hysteresis torque. Therefore, the engine speed fluctuation is sufficiently absorbed and no abnormal sounds occur during driving.
A fluid torque transmission device equipped with a lockup device in accordance with a second aspect of the present invention is the device of the first aspect wherein, the friction generating mechanism is arranged to function in parallel with the elastic connection mechanism of the lockup device between the front cover and the turbine.
In this fluid torque transmission device equipped with a lockup device, the friction generating mechanism is arranged to function in parallel with the elastic connection mechanism. In other words, the friction generating mechanism is provided separate from the elastic connection mechanism making the structure of the lockup device simpler.
A fluid torque transmission device equipped with a lockup device in accordance with a third aspect of the present invention is the device of the second aspect wherein, the turbine includes a turbine shell, multiple turbine blades provided on the impeller side of the turbine shell, and a turbine hub affixed to the inner periphery of the turbine shell. The friction generating mechanism is located in the axial direction between the front cover inner periphery and the turbine hub.
Since the friction generating mechanism is located in an axial direction between the front cover inner periphery and the turbine hub in the fluid torque transmission device, it is possible to make the friction surface abut with other members using the pressure in the fluid chamber. Consequently, it is unnecessary to have a separate member for the purpose of applying load in the friction generating mechanism, thus reducing the number of parts.
A fluid torque transmission device equipped with a lockup device in accordance with a fourth aspect of the present invention is the device of third aspect wherein, the friction generating mechanism has an engagement part that engages with either one of the front cover or the turbine hub across the micro gap in the rotating direction. Further, the friction surface is placed between the engagement part and the other one of the front cover or the turbine hub.
Within the range of the micro gap wherein the engagement part of the friction generating mechanism does not abut against either one of the front cover or the turbine hub in this fluid torque transmission device, the friction surface does not rub against the other one of the front cover or the turbine hub.
A fluid torque transmission device equipped with a lockup device in accordance with a fifth aspect of the present invention is the device according to the fourth aspect that has a thrust bearing placed between the friction generating mechanism and either one of the front cover or the turbine hub.
Since the thrust bearing is placed in the axial direction between the friction generating mechanism and either one of the front cover or the turbine hub in this fluid torque transmission device, the engagement part rotates together with the other one of the front cover or the turbine hub across the friction surface within the micro gap range, in other words, no rubbing occurs on the friction surface. The thrust bearing mentioned here includes those types of bearings having multiple rolling members that carry loads in the axial direction while generating very little friction resistance in the rotational direction.
A fluid torque transmission device equipped with a lockup device in accordance with a sixth aspect of the present invention is the device any one of the first to fourth aspects having a friction generating mechanism, which generates friction smaller than the friction of the friction surface in order to dampen the vibrations of micro twisting angles within the range of micro twisting angles.
These and other objects, features, aspects, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.